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Your Menstrual Cycle, Explained

[Psst...if you're starting here, you should probably read this first!Also, disclaimer: If you don't like talking about women's anatomy and stuff, you have been warned.]

If you're anything like how I used to be, your period was something that just showed up every once in a while. I'd start to get this feeling and think, "Huh...it's probably time for my period again sometime soon. I haven't had it in a while." Then I'd get my period.

Fast forward 3 weeks and repeat.

I didn't really know much beyond that beside the fact that it was a cycle, and at some point during my cycle I could get pregnant. I'd been told by OB-GYN's that there was always a risk for pregnancy at any point during your cycle--whether you're on your period or not.

But mostly, my period was a huge black box of mystery. It came, it went, and then started all over again next month. What happened in between was...well, I had no idea what it was.

Hopefully by the end of this post, you'll know more than you ever thought possible about your menstrual cycle. It's not an exaggeration to say that knowing this information was one of the most empowering gifts of information I have ever received. Instead of a mysterious thing that just happened to me, it became something that I was completely aware of and thus in control of.

So, how can this help YOU? Here are a few ways:

You can know the date of your next cycle without having to worry about it coming during a range of dates (this is especially helpful if your cycles are irregular or unpredictable; even though the first half may vary, the second half of your period is almost always the same length in each individual woman).

You will know several basic pieces of information vital to understanding your potential infertility: Am I even ovulating? Is my luteal phase too short to sustain implantation? Am I getting pregnant and mistaking it for a late period when I miscarry?

If you know when you ovulate, you know exactly when you can and cannot get pregnant each month. No more surprise pregnancies!

I could go on, but hopefully you see why knowing about this could be incredibly helpful to you. If nothing else, I hope you use this to become more aware of your body and yourself. It doesn't matter if you never decide to start charting; knowing about their cycles is information every woman should have.

In this post, we'll be describing a regular menstrual cycle, so this may not apply to women who have variations in their periods due to medication (including hormonal birth control), medical issues such as PCOS or annovulation, or otherwise irregular cycles. We'll talk about special circumstances in later posts.

First of all, we'll need to cover some basic female reproductive anatomy. It's important for you to know your internal and external reproductive anatomy, so even if you think you already know, I'd recommend going over it again anyway. I won't go into detail on the external reproductive anatomy here, but I'd take a look at this diagram if you need to brush up on what's where.

The internal reproductive system should look familiar to you (I hope).

I drew this in Illustrator while Tim was watching tv...needless to say, glancing at a computer screen with a massive uterus on it can be a little startling for husbands. :)

Besides looking like the face of a goat or possibly a really weird alien, your reproductive organs do a lot of really cool things.

Let's briefly go over the above terms, just so we're clear on where everything is:
Your Ovaries contain all of your eggs cells, and are about the size of an almond. When you are born, your body contains all the eggs it will ever produce.
Your Fallopian Tube connects your ovaries to your uterus--this is where the egg will wait for fertilization each cycle.
The Uterus is about the size of an upside-down pear. It's an amazing organ that can expand up to 500 times its regular size during pregnancy, and return back to its original size afterward. If an egg is fertilized, it will implant into the uterus to grow there.
Your Endometrium is a lining of blood that builds up in your uterus every month. If no egg is fertilized, it is shed and becomes your period. If it is fertilized, it grows thicker and helps protect and nourish the fetus.
The cervix is the at the bottom of your uterus. It is a ring of muscle that can expand and contract. There are ducts just inside the cervix that produce cervical fluid when you are about to ovulate.
And let's not forget the vagina! The vagina is the entrance to the cervix and uterus. It also has the ability to expand and contract, as well as produce its own fluids.

An average menstrual cycle is anywhere from 24 to 38 days long. Let's start with Day 1.

FOLLICULAR PHASE: MENSTRUATION TO OVULATION
TheFollicularPhase, or first half of your cycle, can vary in length. It covers the time from the first day of your period until ovulation. The first day of your period is always the first day of your cycle. Usually, your follicular phase is anywhere from one to three weeks long. Because no egg was fertilized in the previous cycle, the unneeded endometrium has begun to shed itself, resulting in your period.

In the first few days of your cycle, the one of the ovaries starts to prepare about 15-20 eggs to be released, each egg encased in its own follicle in the ovary. The immature eggs develop slowly over the course of about two weeks. One egg is chosen to be released, and when it is mature, it bursts through the ovarian wall into the fallopian tube. Tada! Ovulation! The remaining 15-20 eggs that were in development are reabsorbed and disintegrate.

In the days leading up to ovulation, the cervix starts producing fertile cervical fluid. It is this fluid that allows sperm to live up to five days. Without this fluid present, sperm can only survive the acidic environment for a few hours--certainly not long enough to find and fertilize an egg.

The cervix also undergoes changes around ovulation. It widens and withdraws back toward the uterus. It is this change, along with your temperature shift and the presence of fertile cervical fluid, that will help you pinpoint when your ovulation occurs.

Immediately after ovulation (about 1-3 weeks into your cycle), the ovarian follicle that released the egg begins to disintegrate as well. As it dissolves, it releases progesterone, which will continue to be released for the next 12-16 days in the second half of your cycle (your Luteal Phase).

While your ovaries are busy preparing eggs and ovulating in the first few of weeks of your cycle, your uterus is simultaneously preparing itself as well. When your period is over, your body immediately starts to rebuild the endometrium in case of fertilization. The progesterone released by the ovarian follicle (which is now called the corpus luteum) causes the endometrium to thicken and sustain itself to wait for the egg to implant.

The second half of your cycle is called your Luteal Phase.

LUTEAL PHASE: OVULATION TO MENSTRUATION

While the Follicular Phase can vary from cycle to cycle in the same woman, the Luteal Phase is incredibly consistent. The onset of ovulation in the first half of your cycle can be delayed by stress, malnutrition, or illness, but once the luteal phase starts, it is virtually impossible to stop.

This is actually quite handy, though, because the end of the Luteal Phase marks the first day of a new cycle with the arrival of--you guessed it--your period. So, if you know the length of your luteal phase, you will always know the exact date of your next period. No more guessing!

So, let's talk about what happens in your luteal phase. Your luteal phase always starts after ovulation has occurred. The length of the luteal phase is usually anywhere from 12-16 days, although it can be as short as ten. Each woman's luteal phase length will remain consistent from cycle to cycle. Mine is always about 10-11 days, but yours may be a different length. Anything shorter than ten days can make it problematic to conceive, because it doesn't give the egg time to properly implant in the endometrium.

The length of the luteal phase is determined by the amount of progesterone released by the corpus luteum (remember that guy? The follicle that released the egg?). Like we talked about earlier, when the egg enters the fallopian tube, the corpus luteum stays behind and releases progesterone. It is this hormone that sustains the endometrium in case of implantation and pregnancy, causes changes in the cervix, and signals the cervix to start producing fertile cervical fluid.

The egg will only live for about 24 hours from the time it is released. Progesterone quickly prevents the release of multiple eggs after a 24-hour period, so that means that about two days after ovulation, you are completely infertile with no chance of pregnancy (until your next ovulation, of course).

Once the egg dies, the progesterone continues to be released by the corpus luteum for the length of the luteal phase. If the egg were to be fertilized, it is this luteal phase that would give the newly fertilized egg time to travel down the fallopian tube, enter the uterus, and implant into the endometrium to grow into a fetus. If implantation happens, the corpus luteum continues to release a hormone, but this time it is the more well-known hCG--the hormone that is used in pregnancy tests to determine if you are pregnant or not. This hormone suspends ovulation and tells the body to sustain the pregnancy.

If conception and implantation don't occur, the progesterone decreases. When no implantation is found, no hCG is produced and your body sheds the endometrium at the end of your luteal phase. You start a new cycle with the beginning of your period.

Phew! We made it!! Your entire menstrual cycle, explained! That wasn't so bad, was it?

(Don't answer that.)

I'm planning on doing a video explainer of your menstrual cycle as well. As my sister wisely pointed out, it can be tough to visualize all the changes that are happening by reading a blog post. Hopefully I'll have that up within a week or so!

In the meantime, questions or comments are always welcome! If you're still confused about your cycle or have questions about something I didn't cover, please reach out and ask. I'd love to hear from you! You can find me on Twitter or Instagram at @know_fertility. I've had some really great questions from you already, and I love getting to hear about your stories, questions, and concerns. Keep it coming!

My next post will be about the how to's of actually charting your cycle. Now that we've gone over a lot of the basics, we're ready to actually dive in to charting. Are you ready? I'm so ready!